1. Field of the Invention
This invention relates to improvements in a plastic bumper for an automotive vehicle, and more particularly to a plastic bumper shaped to be light in weight and made of a material to cause the bumper to exhibit excellent performance in: resistance upon a light collision, shape maintenance characteristics over a long period of time and gloss and brightness character of a paint coated on the bumper.
2. Description of the Prior Art
Over ten years have lapsed since the material used in bumpers of automotive vehicles changed from steel to plastic. However, no fundamental change in structural mode has been heretofore made in such plastic bumpers, so that progress has been made only in improvement in moldability, shape, dimensional stability and paintability. Examples of such plastic bumpers are shown in FIGS. 1 and 2 and described in detail in Table 1 of the present invention. In FIG. 1, a bumper 1 includes a main body 2 made of plastic. A reinforcement member 3 made of metal is fixedly fitted in the main body 2 and connected to a vehicle body through stays 4. In FIG. 2, a bumper 1' includes a main body 2 which is formed with vertical ribs 5 and horizontal ribs 6. The ribs 5,6 are connected through stays 4 to a vehicle body.
However, difficulties have been encountered in these types of bumpers, in which it is essential to use the reinforcement member while increasing the weight of the bumper. Owing to this, a further weight-lightening requirement for automotive vehicles have not been able to met, thereby preventing progress in weight-lightening of the vehicles. Additionally, such conventional bumpers are problematic because it is difficult to obtain a flat surface without sinkage due to resin shrinkage at ribs, high shape maintenance characteristics over a long period of time and a high gloss and brightness character of a paint film coated on the plastic bumper.